The invention relates to determining the hematocrit of a whole blood sample, specifically through the use of a biosensor and electrochemical techniques.
Hematocrit is the volume of red blood cells expressed as a percentage of the volume of whole blood in a blood sample. Hematocrit is used clinically to characterize blood. A low hematocrit indicates anemia (a low number of red blood cells and thus a reduced capacity for the blood to carry oxygen) and a high hematocrit may indicate polycythemia (a high number of red blood cells which may be a warning signal of serious circulatory failure). Hematocrit determination in the lab may provide an early diagnosis of these conditions.
U.S. Pat. No. 4,068,169 (Angel et al.), issued Jan. 10, 1978, discloses the measurement of hematocrit by passing a diluted volume of blood through sensing means, wherein conductivity changes in response to the presence of red blood cells passing through the sensing means.
U.S. Pat. No. 4,547,735 (Kiesewetter et al.), issued Oct. 15, 1985, discloses a hematocrit measuring device that includes upper and lower spatially displaced electrodes. A blood sample is added to the device and hematocrit level is correlated to changes in impedance of the blood sample.
U.S. Pat. No. 4,699,887 (Abbott et al.), issued Oct. 13, 1987, discloses a method of measuring the hematocrit level of blood by measuring the concentration of a marker (i.e. sodium ion) that has a different concentration in red blood cells versus plasma before and after lysing the red blood cells. The change in concentration of the marker after lysis can be correlated to the hematocrit level in the original blood sample.
U.S. Pat. No. 4,876,205 (Green et al.), issued Oct. 24, 1989, discloses an electrochemical assay for hemoglobin, wherein red blood cells are lysed and hemoglobin is assayed by monitoring the current changes produced on reduction of ferricyanide to ferrocyanide by hemoglobin.
U.S. Pat. No. 3,922,598 (Steuer et al.), issued Nov. 25, 1975, discloses an electrochemical apparatus for measuring hematocrit level of whole blood. The apparatus includes a pair of electrodes, a constant current source, and is calibrated so a plasma sample will give a reading of zero. When a probe is exposed to whole blood, the output voltage swings negatively. The magnitude or* this negative swing in voltage may be correlated to hematocrit level.
In addition, U.S. Pat. No. 4,835,477 (Metzner et al.), issued May 30, 1989, U.S. Pat. No. 4,686,479 (Baumeister et al.), issued Aug. 11. 1987, U.S. Pat. No. 4,303,887 (Hill et al.), issued Dec. 1, 1981, U.S. Pat. No. 4,301,412 (Hill et al.), issued Nov. 17, 1981, and U.S. RE 30007 (Enke et al.), issued May 22, 1979, all use conductivity measurements to determine the hematocrit level of a blood sample.
European Patent Application Publication No. 417796A (Ishihara), published Mar. 20, 1991, discloses an instrument which uses impedance to measure the hematocrit of a blood sample.
The STAT-CRIT.RTM. device, a commercial hematocrit and hemoglobin measuring instrument, performs a hematocrit measurement based on blood resistivity, which increases as hematocrit increases.